Splitter with Adaptive Power Distribution

ABSTRACT

The invention relates to a splitter of an indoor cellular network, with a plurality of antennas transmitting downlink signals and receiving uplink signals, the splitter distributing power to said plurality of antennas for a transmission of the downlink signals. The splitter adapts the signal power of the downlink signal for one antenna in accordance with the uplink signal received at said antenna.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/265,299, which was filed on Jan. 11, 2012, which is anational stage application of PCT/EP2009/054291, filed Apr. 9, 2009, thedisclosures of each of which are incorporated herein by reference intheir entirety.

TECHNICAL FIELD

This invention relates to a splitter connected to a plurality ofantennas of an indoor cellular network and to a method for controlling apower distributed via the splitter to a plurality of antennas of theindoor cellular network.

BACKGROUND

Indoor cellular systems are becoming increasingly spread, as userdemands for everywhere coverage are matched by the opportunity formobile operators to offer improved services and increase trafficrevenues. The owners of the building, in which the indoor cellularsystem is provided, also benefit from such a system, as the value oftheir property and their ability to attract and retain key tenantsincreases.

It is estimated that two thirds of all calls are made from inside abuilding and, with the increased demands for high data trafficcapabilities, there is a growing need for improved capacity and coveragefrom indoor users.

An in-building cellular system offloads surrounding macro sites andensures a higher quality of service for indoor users.

One of the basic components provided in a distributed antenna system(DAS) is the power splitter, which divides the power from a radio basestation, NodeB or eNodeB for distribution to several antennas. Thesplitter distributes the signal equally to multiple antennas and isnormally a passive component that has one input and several outputs. Thesplitter is an RF component which cannot amplify the input signal andsplits it at the output only. By way of example, in case of a 2-waysplitter, the splitter splits the input signal power into two equaloutput powers, whereas, in case of a 3- or 4-way splitter, the splittersplits the input signal in three and four equal output power signals,respectively. The 4-way splitter, by way of example, splits power fed atits input equally to each of the four antennas connected to therespective output port.

In FIG. 1 a splitter 10 as known in the prior art is shown in furtherdetail. The splitter 10 comprises an input port 11 to which the totalpower P_(total) is fed for distribution to different output ports 12.The splitter shown in FIG. 1, a 3-way splitter, comprises three outputports 12 to which the total power P_(total) is distributed. In thesplitter shown the power is equally distributed to each output port withP_(total)=P1+P2+P3 with P1=P2=P3.

This traditional splitter does not consider the traffic load at theantennas connected to the different output ports so that the power willbe split independently of the number of mobile stations connected to theantennas.

Furthermore, antenna problems can cause a significant degradation ofcoverage in cells of the network. It is very difficult and costly for anoperator to detect these antenna problems, unless they cause severe andacute radio problems. As a consequence many antenna installationproblems are hidden for the operator or are mistaken for general cellplan issue, interference problem or even a problem with radio networkfunctionality.

With the current architecture of an indoor cellular network it is notpossible to optimize the power and to manage the power distributionflexibly in terms of carried traffic by each antenna. As a consequence amajor part of the radio base station power is wasted in the buildingdistributed antenna system.

Additionally, antenna problems can only be found easily, when theantenna is directly connected to the radio base station as it is thecase for outdoor cellular systems. In case of an indoor cellularnetwork, antennas are normally not directly connected to the radio basestation. They are connected to the radio base station through MCM (MultiCasting Matrix) and splitters/tapers. Antennas and feeders which areconnected to chain of passive components, such as splitters or tapers,cannot be detected.

SUMMARY

Accordingly, a need exists to be able to effectively manage the powerdistribution of an indoor cellular system and to be able to detectfaulty antennas of an indoor cellular network in an efficient way.

These needs are met by the features of the independent claims. In thedependent claims further embodiments of the invention are described.

According to a first aspect of the invention, a splitter connected to aplurality of antennas of an indoor cellular network is provided, theantennas transmitting downlink signals and receiving uplink signals. Thesplitter distributes power to said plurality of antennas for thetransmission of the downlink signals, wherein the splitter comprises asignal determining unit that is determining for one of the antennas asignal strength of the uplink signal, wherein the splitter is adapted todistribute the power to said one antenna for transmitting the downlinksignal in accordance with the signal strength of the uplink signalreceived by said one antenna. The splitter is able to control thetransmitted power transmitted to said one antenna and to adapt thetransmitted power in proportion to the received power. If in an areacovered by one antenna a weak traffic is noticed, the transmitted poweris reduced proportionally. The signal determining unit measures thesignal strength of the uplink signal received by an antenna connected toone output port of the splitter, the splitter adapting the signal powerfor the downlink signal for said output port accordingly. With such asplitter the transmitted total power can be efficiently used in such away that more and more antennas can be used to cover a building, sincethe power can be intelligently split in all building areas depending onthe carried traffic by each antenna. Additionally, there is no need touse power tapers in that distributed antenna system, since theintelligent splitter can split the power efficiently. Furthermore, lessradio base stations are needed in view of the optimized powerdistribution, as a single radio base station can serve a larger numberof antennas.

According to a preferred embodiment of the invention, the splitter isconfigured in such a way that it distributes the power to each of theantennas connected to the splitter in accordance with the respectiveuplink signal of the antennas. The intelligent splitter controls thepower flows at each output port depending on the carried traffic by eachof the antennas connected to the corresponding output port. In case thisflexible power distribution is used in substantially all the splittersof an indoor cellular system, a considerable amount of power can besaved at some of the antennas and distributed to other antennas where itis more needed.

Preferably, the signal determining unit determines the signal strengthof the uplink signals originating from a predetermined part of thebuilding in which the indoor cellular network is installed. By way ofexample, the signal determining unit may determine the uplink signalstrength of mobile stations provided in a room in which said antenna isprovided. The splitter preferably distributes to each antenna a signalfor the downlink signal having a signal strength that is proportional tothe respective uplink signal strength. This means, when the uplinksignal strength for one of the antennas connected to the splitter willbe high and will be lower for another antenna of the splitter, thedownlink signal will be higher for said one antenna than for said otherone.

Preferably, the splitter is configured in such a way that the splitterdistributes to each antenna a downlink signal with a minimum power.Normally the uplink signal will never be exactly zero, since there isthe uplink signal received by the antenna due, for example, toreflection of other uplink signals received from mobile stations locatedat larger distances. Furthermore, the control channels provided in theindoor cellular network will not be affected, since there will be aminimum power transmitted from a radio base station via the splitter toeach of the antennas.

For adjusting the power distributed by the splitter to one of theantennas the splitter may comprise an automatic load adjusting unitadjusting the power distributed to said one antenna. The load adjustingunit then automatically adjusts the load of the output port connected tosaid one antenna in accordance with the uplink signal strength receivedby said one antenna. Based on the uplink signal strength determined bythe signal determining unit a port load of the output port, to whichsaid one antenna is connected, is adjusted automatically. The signaldetermining unit can periodically update the automatic load adjustingunit with the latest measured signal strength values of the uplinksignal requesting the automatic load adjusting unit to adjust thecorresponding load value for the output port, to which said antenna isconnected. By way of example, in case the received uplink signalstrength is weak, the port load may be adjusted too low, e.g. 5 Ohm ormore, as, in this case, the reflection factor is approximately R=0.82.If the received signal strength of the uplink signal is high due to moreusers or mobile stations provided on the antenna cell, the port load maybe adjusted to a high value, e.g. 48 Ohm or less, as, in this case, thereflection factor will be low, e.g. R=0.02.

The signal determining unit is configured to determine, for said oneantenna, the signal strength of each uplink signal picked up by said oneantenna separately and to sum up the signal strength to a combineduplink signal strength. The splitter then adapts the signal strength forthe downlink signal in accordance with the signal strength of thecombined uplink signal strength. Furthermore, the signal determiningunit may synchronize the different uplink signals received by said oneantenna before the combined uplink signal strength is determined. Thecombined uplink signal strength can be determined periodically andtransmitted as periodic signal strength of the uplink signal to theautomatic load adjusting unit that is adjusting the load of the downlinksignal, accordingly.

Preferably, the splitter comprises a signal determining unit determiningthe signal strength of the uplink signal for each output port of thesplitter.

The splitter can be connected to different antennas at its output ports,however, it is also possible that the splitter, at one of its outputports, is connected to another splitter. In this situation the splitterdistributes the power to said one output port, to which the othersplitter is connected, depending on the uplink signals received byantennas connected to said other splitter. Furthermore, it is possiblethat more than one or all output ports of the splitter are connected toother splitters, the splitter distributing the power to its output portsdepending on the respective uplink signals received by the antennasconnected to the other splitters.

For visualizing and monitoring the status of the antennas or RF devicesconnected to the output ports of the splitter the splitter mayfurthermore comprise a monitoring unit for at least one of its outputports, the monitoring unit monitoring the functioning of an RF deviceconnected to said at least one output port. This monitoring unit candetect non-working antennas and damaged feeders and send an alarm signalindicating that the RF device connected to said output port is notworking properly. Preferably, the monitoring unit transmits a testsignal periodically to the RF device connected to said one output portand analyzes the feedback signal received in response to the test signalin order to determine whether the RF device connected to said at leastone output port is functioning properly or not. By way of example, themonitoring unit may measure the standing wave ratio (SWR) of thereceived feedback signal of each connected RF device at the splitterport. The monitoring unit can then compare the measured SWR value to apredetermined SWR value registered in it.

Preferably, the splitter furthermore comprises a monitoring port towhich said alarm signal output by the monitoring unit is transmitted,when the monitoring unit has detected that the RF device connected tosaid at least one output port is not functioning properly. From themonitoring port the alarm signal may be transmitted to a central controlunit, where the status of the different antennas and splitters ismonitored.

The invention furthermore relates to a method for controlling the powerdistributed by the splitter to the plurality of antennas, the methodcomprising the steps of determining, for one of the antennas, a signalstrength of the uplink signal, in the splitter, wherein the power tosaid one antenna for transmitting the downlink signal is distributed inaccordance with the signal strength of the uplink signal received bysaid one antenna. As discussed above this method allows to efficientlysplit the power to the different antennas of the indoor cellular system.Preferably, the power is distributed to each of the antennas connectedto the splitter in accordance with the respective uplink signal of thedifferent antennas. As several mobile stations may transmit signals tothe antenna, the signal strength of each uplink signal received by saidone antenna can be detected separately and summed up to a combineduplink signal strength for said antenna, the signal strength distributedto said one antenna for the downlink signal being in proportion to thecombined uplink signal strength. Preferably, the power distribution tosaid one antenna is controlled by adjusting the load of the splitteroutput port in dependence on the signal strength of the uplink signal.

For monitoring the status of the different RF devices of the indoorcellular system it is possible to transmit a test signal to at least oneof the output ports of the splitter and to receive a feedback signalfrom said output port and to evaluate the status of the RF deviceconnected to said output port using the feedback signal. The status canbe evaluated by comparing the feedback signal to a predetermined value.An alarm signal can then be generated, when it is detected that thefeedback signal differs from said predetermined value by a predeterminedamount. The alarm signal can furthermore be displayed on a display wherethe defects of a plurality of RF devices of said indoor cellular systemare summarized and visualized.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention further objectives and advantages thereof will best beunderstood by reference to the following detailed description ofillustrative embodiments, when read in conjunction with the accompanyingdrawings, wherein

FIG. 1 shows a splitter according to the prior art,

FIG. 2 shows a schematic view of an indoor distributed antenna systemallowing to efficiently distribute the power and allowing to monitor theantennas of the system,

FIG. 3 shows an exemplary view of a display with which the functioningof the RF devices of the indoor cellular system can be visualized,

FIG. 4 shows a splitter allowing to efficiently distribute the power toits output ports,

FIG. 5 shows an embodiment of the indoor cellular system with antennasin different rooms,

FIG. 6 shows the distribution of power in the splitter for theembodiment shown in FIG. 5,

FIG. 7 shows a more detailed view of a filter contained in the splitteradapting the downlink signal strength in accordance with the receiveduplink signal strength,

FIG. 8 shows a flow-chart comprising the steps for processing the uplinksignal in the splitter,

FIG. 9 shows another embodiment of a distributed antenna indoor systemwith different traffic load in different rooms,

FIG. 10 shows the splitter with a power distribution in an embodiment asshown in FIG. 9,

FIG. 11 shows an embodiment with several splitters in a cascadedconnection,

FIG. 12 shows power distribution for an embodiment as shown in FIG. 11,

FIG. 13 shows another embodiment for distributing power to each of itsoutput port depending on the received uplink signal strength, and

FIG. 14 shows a splitter monitoring the functioning of an antennaconnected to one of the output ports.

DETAILED DESCRIPTION

In FIG. 2 a schematic view of a distributed antenna system of an indoorcellular system is shown. The system shown distributes power from aradio base station or base station transceiver 22 to a plurality ofantennas 13 via power splitters 40. The antennas 13 may be provided indifferent rooms and/or different levels of the building in which thesystem shown in FIG. 2 is provided. The power from the radio basestation is transmitted to the different splitters 40 via Multi CastingMatrix unit 24. Furthermore, a network control unit 20 is providedcontrolling the proper functioning of the indoor cellular system and ofthe RF devices, in particular the antennas. Each of the splitter isconnected, e.g. via a twisted pair cable through a monitoring port 47 ofthe splitter shown in FIG. 4 to a control matrix 23 of the distributedantenna system. The functioning of the monitoring port will be explainedin further detail later on with reference to FIGS. 6 and 14. The controlmatrix 23 is connected via a network control interface 27 of the radiobase station to the network control unit 20. By way of example, thecommunication between the radio station and the network control unit canbe carried out over an IP network, e.g. using the ATM (AsynchronousTransfer Mode) data transmission technology, ATM being a packetswitching protocol encoding data into small, fixed-sized cells.

As can be seen from FIG. 2 the antenna 13 may be directly connected tothe splitter, however, the splitter may also be connected to anothersplitter resulting in a cascaded arrangement of splitters. In theembodiment shown in FIG. 2 three antennas are connected to one splitter.However, it should be understood that the number of antennas could beconnected to one splitter, by way of example, the splitter may have two,three or four antennas connected to the different output ports of thesplitter (not shown in FIG. 2).

In FIG. 4 the splitter 40 is shown having an input port 46, where thetotal power distributed P_(total) is received. The splitter, in theembodiment shown, is a 4-way splitter having four output ports 41 to 44.At each of the output ports an intelligent electronic filter 45 isprovided adapting the power of the downlink signal for each of theoutput ports depending on the received uplink signal strength receivedat each of the output ports. The splitter furthermore comprises amonitoring port 47, which will be discussed in further detail below inconnection with FIG. 14. The filter 45 at each of the output ports isable to variably adjust the load of each output port.

In FIG. 5 a first example of an indoor cellular system distributingpower depending on the received uplink signal strength is shown. In theembodiment shown the splitter 40 is connected to four different antennas13 in four different rooms. In each room three mobile stations areprovided, all the mobile stations having line of sight with thecorresponding antenna. When each of the mobile stations is in an activemode, the signal is transmitted to the splitter having a signal strengthof RxLev1 for the first room, RxLev2 for the second room, RxLev3 for thethird room and RxLev4 for the fourth room.

As also shown in FIG. 6 the filter 45 provided at each output portdetermines the uplink signal strength at the output port, where it isprovided, and lets pass the proportional signal strength or signal powerto the mobile station. In the embodiment shown in FIGS. 5 and 6 it isassumed that all antennas are in the dedicated mode so that each mobilestation sends RxLev power to the antenna. In the embodiment shown inFIGS. 5 and 6 this means that total RxLev at each antenna is the same,as the number of mobile stations in each room is the same. As aconsequence the power distributed to each of the filters provided in thefour different output ports is the same with Ptotal=P1+P2+P3+P4 withP1=P2=P3=P4.

In FIG. 9 another situation is shown in which no mobile phone in thededicated mode is present in room 3 whereas two mobile phones arepresent in room 1 and three mobile phones are present in room 2 and 4.As also shown in FIG. 10 each filter measures the RxLev uplink signalstrength sent by all mobile phones in each room and lets pass theproportional Px signal or signal power to the mobile stations. With thenumber of mobile stations being present as shown in FIG. 9, the uplinksignal strength of room 4 will correspond to the uplink signal strengthof room 2. The uplink signal strength of room 1 will be smaller than theuplink signal strength of room 2 and 4, whereas substantially no uplinksignal strength will be detected by the antenna present in room 3 exceptlow signals from the mobile stations provided in other rooms. The filter45 provided at each output port of the splitter will adapt the downlinksignal for each of the antennas in accordance with the received uplinksignal strength. Thus, the highest power will be fed to the antennaspresent in rooms 2 and 4, whereas a smaller amount of power istransmitted to room 1 and a minimum amount of power is transmitted tothe antenna present in room 3. Even though the distributed powerdistributed to room 3 is shown to be zero by a crossed-out arrow itshould be understood that a predetermined minimum power is transmittedin the splitter to the corresponding output port and to antenna 13provided in room 3.

A schematic view of the filter 45 adapting the power of the downlinksignal is shown in further detail in FIG. 7. The uplink signal receivedat a splitter output port 41 is first transmitted to a band pass filter452 that is adapted to let pass the frequency band used in the mobilestations, the band pass filter blocking the other frequencies. The bandpass filter 452 reduces the signal processing load in the otherprocessing units provided in the filter 45, as only the relevant uplinksignals will be able to reach a decoder 454 that decodes the filteruplink signal. This decoder 454 helps to demodulate the uplink signallater on by a demodulator 455 and decodes the received uplink signal.The decoder 454 should know the coding system used by the mobilestations and by the radio base station. The decoder can be informed ofthe coding system by the mobile station in the uplink signal and by theradio base station in the downlink signal. The decoder furthermoresynchronizes each signal received in order to determine the start andthe end bits of each uplink signal. From the decoder 454 the signal isthen transmitted to the demodulator 455 demodulating the uplink signalso that it can be measured by the digital signal determining unit 456.The demodulator 455 should know previously which type of modulation hasbeen used by the mobile station in order to be able to demodulate theuplink signal correctly.

In the signal determining unit 456 the signal strength of the uplinksignal is determined. The signal determining unit 456 digitizes eachuplink signal separately and synchronizes each signal with the knownstart and end bits of each received signal. The signal strength orsignal intensity of all modulated uplink signals is then determined andsummed up in order to obtain a combined uplink signal strength. Thiscombined uplink signal strength is determined periodically and iscommunicated periodically to an automatic load adjusting unit 453 asshown by the dash-dot line. The automatic load adjusting unit 453adjusts the load of the output port in order to adjust the downlinksignal received from the splitter input port 46. The automatic loadadjusting unit regulates the port load automatically from a low value εOhm to 50 Ohm, E being a parameter for a low value, e.g. between 1 and10 Ohms, 50Ω being the impedance of the connected cable and the antenna.The load values are determined by comparing the determined combineduplink signals to predefined signal strength values and to deducetherefrom corresponding load values contained in a database provided inthe filter 45. By way of example, the automatic load adjusting unit mayperiodically calculate the voltage standing wave ratio (VSWR) to adaptthe load of the output port. As it is known in the art the most powercan be transmitted to an antenna when the impedance of the antennacorresponds to the impedance of the feeding cable and the impedance ofthe output port, to which the feeding cable of the antenna is connected.Accordingly, if a high signal power should be transmitted to an antenna,an impedance of close to 50 Ohms should be used at the correspondingoutput port, to which the antenna is connected, when the independence ofthe antenna and the feeding cable is 50Ω. The automatic load adjustingunit adjusts the load of the output port. After the combined uplinksignal strength has been determined, the signal will be forwarded to themodulator 457 for further processing and to fit the RF propagationrequirements of the next transmission channel, which may be a feedercable. The modulation used (8PSK, QAM-16, QAM-64) should be similar tothe one used by the mobile station. This is advantageous in order toavoid any incompatibility of the signal processing at the radio basestation later on. From the modulator 457 the signal is transmitted tothe coding unit 458 where the signal is secured by coding it. The codingis carried out to avoid any wiretapping attack of the signal between thesplitter's port and the RF component connected to the input port 46towards the radio base station.

The signal path of the downlink signal is shown in the dashed line. Inthe downlink the signal will neither be decoded nor demodulated ormeasured. The downlink signal will be simply forwarded inside thesplitter from the splitter input port 46 to the automatic load adjustingunit 453, where it is attenuated depending on the load value adjustedand generated by the load adjusting unit in accordance with the combineduplink signal strength as determined by the signal determining unit 456.The adjusted load value should play the role of a traditional physicalpassive load that can be screwed to the splitter port. After attenuationof the downlink signal depending on the signal strength of the combineduplink signal strength, the former is forwarded to the splitter outputport 41 to propagate to the RF components connected to this port.Furthermore, a power supply unit 451 is provided providing power to thedifferent units via feeder cables used to connect all other filtercomponents to each other. The power consumption will be minimized as thefilter components are only processing the signal. They are notamplifying the signal, so a high power as power supply is not needed.The functioning of monitoring unit 459 of FIG. 7 will be explained indetail later on.

In FIG. 8 the signal processing steps carried out on the uplink signalare summarized. In step 81 the uplink signal received from the splitteroutput port is band pass filtered. After filtering the signal the uplinksignal is decoded in step 82 and demodulated in step 83. For retrievingthe RxLev from each mobile station the uplink signal has to be decodedand demodulated. After the decoding and the demodulation the signalstrength can be determined in step 84 wherein the signal strength ofeach uplink signal is determined, the signal being synchronized and acombined uplink signal strength being determined. In step 85 the signalis modulated again and coded in step 86 before it is transmitted to thesplitter input port 87 for further transmission to the radio basestation.

In FIG. 11 a cascaded view of a splitter arrangement is shown. Asplitter 40-1 is connected at the first output port to splitter 40-2 andat the second output port to splitter 40-3. Splitter 40-2 has threeoutput ports, whereas splitter 40-3 has four output ports. Splitter 40-2receives the uplink signal S2RxLev1, S2RxLev2 and S2RxLev3, the totaluplink signal RxLev_(total)-S2 being transmitted to the first outputport of splitter 40-1.

The splitter 40-3 receives uplink signals S3RxLev1, S3RxLev2, S3RxLev3and S3RxLev4, the total uplink signal strength being RxLev_(total)-S3received at the second output port of splitter 40-1. Splitter 40-1 nowdistributes the total power P_(total) in accordance with the signalstrength of RxLev_(total)-S2 ^(and) RxLev_(total)-S3 by adapting S1P1and S1P2 accordingly. Summarizing, each filter provided in the splitters40-2 and 40-3 measures the RxLev uplink signal sent by all mobilestations and let pass the proportional downlink signal. In FIG. 12 theembodiment shown in FIG. 11 is shown in another situation, wheresubstantially no uplink signal is received by the three antennasconnected to the splitter 40-2. In this situation splitter 40-2 will getminimal Tx signal/power because all antennas at its ports are carryingsubstantially no traffic. Therefore, the receiving signal RxLev comingfrom splitter 40-2 is very low. As a consequence the transmitted powerS1P1 will also be very low.

In FIG. 13 another embodiment is shown. In this embodiment the receiveduplink signal RxLev3 received at filter F3 is lower than the uplinksignal strength RxLev2 received at filter F2, which itself is lower thanthe uplink signal strength RxLev4 received at filter F4. The strongestuplink signal strength is received at filter F1 by RxLev1. Thedistribution of the total power P_(total) distributed to the differentoutput ports by the filters is indicated by the different arrows havinga thickness proportional to the signal strength received at thecorresponding input port. As discussed above, in case of a weak uplinksignal, the port load will be adjusted low, close to 5 Ohms or lessresulting in a high reflection factor R=0.82. For a strong uplinksignal, such as RxLev1, the port load will be adjusted to a high value,e.g. 48 or 50 Ohm, resulting in a low reflection factor R=0.02.

In connection with FIG. 14 the monitoring unit 459 shown in FIG. 7 isexplained in further detail. The intelligent filter furthermore monitorsthe RF devices connected to its output port. To this end each filter 45has a monitoring unit 459 transmitting a test signal as shown in FIG. 14to the antenna via the feeder cable. The monitoring unit then measuresthe standing wave ratio of the received feedback signal of eachconnected RF device at said splitter port. The monitoring unit 459 thencompares the measured SWR value with known predetermined

SWR values. In case the measured SWR value of the feedback signal is notequal to the predetermined value or differs from said predeterminedvalue by more than a predetermined amount, the monitoring unit generatesan alarm signal and forwards it to the monitoring port 47 provided inthe splitter and further through a cable, e.g. a twisted pair cable, tothe control matrix 23, in which each splitter is connected to one port.The control matrix comprises several connectors on its front side. Eachmonitoring port of a splitter is connected with only one port of thecontrol matrix. The control matrix is directly connected to the networkcontrol unit 20 via interface 27 in the base station via a LAN cable.The interface 27 at the radio base station is connected to the networkcontrol unit via the ATM network, IP network or others. The status ofeach RF device, connected to each splitter output port can be monitoredand visualized on an alarm visualizing tool. The alarm visualizing toolmay be a software provided on the network control unit that is able todisplay and indicate the exact location of the alarm source in thedistributed antenna system as shown in FIG. 3. Furthermore, the detailsof each RF device connected to the different splitter ports, such as thestatus, the type, the name and location of the RF device, can bevisualized in the alarm visualizing tool. In the embodiment shown inFIG. 3 some of the dots indicate a not properly functioning RF device.In the examples shown the filled data points 31 indicate faulty devices,whereas the non-filled data points 32 show components that are operatingcorrectly. By way of example, the visualizing tool may be designed insuch a way that by clicking on the different circles shown in FIG. 3 awindow may be opened where the data of the dedicated component areindicated.

1. A splitter for an indoor cellular network configured to distribute downlink signal power amongst output ports of the splitter, wherein the splitter comprises one or more electronic filters configured to: determine, for each of the splitter's output ports, a traffic load at one or more antennas directly or indirectly connected to that output port; and adjust the proportion of downlink signal power distributed to each of the splitter's output ports in dependence on the traffic load determined for that port.
 2. The splitter of claim 1, further comprising, for each output port, an automatic load adjusting circuit configured to adjust the proportion of downlink signal power distributed to the port by adjusting an impedance of the port.
 3. The splitter of claim 1, wherein the proportion of downlink signal power distributed to each output port is directly proportional to the traffic load determined for that port, the proportion of downlink signal power distributed to the port being related to said traffic load by a non-zero constant multiplier.
 4. The splitter of claim 1, wherein the splitter is connected to another splitter at one of said output ports, and wherein the splitter is configured to distribute power to said one output port in dependence on a traffic load at one or more antennas connected to said another splitter.
 5. The splitter of claim 1, configured, for at least output port, to monitor a functioning of an RF device connected to said at least one output port.
 6. The splitter of claim 5, configured to periodically transmit a test signal to the RF device and to analyze a feedback signal received in response to the test signal in order to determine whether or not the RF device is functioning properly.
 7. The splitter of claim 5, further comprising a monitoring port, and wherein the splitter is configured to transmit an alarm signal to the monitoring port responsive to detecting that the RF device is not functioning properly.
 8. A splitter for an indoor cellular network configured to distribute downlink signal power amongst output ports of the splitter, wherein the splitter comprises one or more electronic filters configured to: determine, for each of the splitter's output ports, a number of mobile stations that are within a coverage area of one or more antennas connected to the output port; and adjust the proportion of downlink signal power distributed to each of the splitter's output ports in dependence on the number of mobile stations determined for that port.
 9. The splitter of claim 8, wherein the one or more electronic filters are configured to determine the number of mobile stations within the coverage area of one or more antennas connected to each output port by measuring signals transmitted in the uplink from the one or more mobile stations.
 10. A method of controlling power distributed by a splitter for an indoor cellular network, comprising: determining, for each of the splitter's output ports, a traffic load at one or more antennas directly or indirectly connected to that output port; and adjusting the proportion of downlink signal power distributed to each of the splitter's output ports in dependence on the traffic load determined for that port.
 11. The method of claim 10, further comprising, for each output port, adjusting the proportion of downlink signal power distributed to the port by adjusting an impedance of the port.
 12. The method of claim 10, wherein the proportion of downlink signal power distributed to each output port is directly proportional to the traffic load determined for that port, the proportion of downlink signal power distributed to the port being related to said traffic load by a non-zero constant multiplier.
 13. The method of claim 10, wherein the splitter is connected to another splitter at one of said output ports, and wherein the method comprising distributing power to said one output port in dependence on a traffic load at one or more antennas connected to said another splitter.
 14. The method of claim 10, further comprising, for at least output port, monitoring a functioning of an RF device connected to said at least one output port.
 15. The method of claim 14, comprising periodically transmitting a test signal to the RF device and analyzing a feedback signal received in response to the test signal in order to determine whether or not the RF device is functioning properly.
 16. The method of claim 14, further comprising a monitoring port, and wherein the method comprises transmitting an alarm signal to the monitoring port responsive to detecting that the RF device is not functioning properly. 